Chip attachment system

ABSTRACT

Forming the chip attachment system includes obtaining a chip having a bump core on a die. The method also includes obtaining an intermediate structure having a transfer pad on a substrate. The method further includes transferring the transfer pad from the substrate to the bump core such that the transfer pad becomes a solder layer on the bump core.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/032,161, filed on Aug. 1, 2014, and incorporatedherein in its entirety.

FIELD

This invention generally relates to attachment of electronic componentsand more particularly to solder bumps.

BACKGROUND

Flip chip mounting refers to a method of mounting a semiconductor chipon an external device. The semiconductor chip is flipped so the activeside of the chip faces the external device and the flipped chip isbonded to the external device. One method of making this attachmentpositions gold bumps on contact pads located on the active side of theflip chip. Thermocompression is used to bond the gold bumps to contactpads on the external device. The gold bumps can then act as anelectrical pathway between the flip chip and the external device. Forinstance, the gold bumps can provide electrical communication betweenthe contact pads on the external device and the contact pads on the flipchip. Temperature cycling of the resulting device can cause the bondbetween the gold bumps and the pads to break. As a result, there is needfor an improved method for attaching electrical components to oneanother.

SUMMARY

A flip chip includes a contact pad on a die. A chip bump is on thecontact pad. The chip bump includes a solder layer on a bump core. Insome instances, the bump core is between the solder layer and thecontact pad.

The flip chip can be formed using a chip precursor that has a bump coreon a die. An intermediate structure is also used. The intermediatestructure has a transfer pad on a substrate. The transfer pad istransferred from the substrate to the bump core such that the transferpad becomes the solder layer on the bump core.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is top view of a flip chip.

FIG. 1B is cross section of the flip chip shown in FIG. 1A taken alongthe line labeled B in FIG. 1A. The chip includes multiple contact padson a die.

FIG. 1C is a cross section of a bump core formed on the contact pad ofFIG. 1B such that the contact pad is between the bump core and the die.

FIG. 1D is a cross section of a multi-layer bump core formed on thecontact pad of FIG. 1B

FIG. 2A and FIG. 2B illustrates an intermediate structure for use informing a chip bump on the flip chip. FIG. 2A is a top view of theintermediate structure. The intermediate structure includes solder on asubstrate.

FIG. 2B is a cross section of the intermediate structure shown in FIG.2A taken along the line labeled B in FIG. 2A.

FIG. 3A illustrates a solder transfer system that includes the portionof the flip chip of FIG. 1C aligned with the portion of the intermediatestructure shown in FIG. 2B.

FIG. 3B illustrates the solder transfer system of FIG. 3A with theintermediate structure contacting the flip chip.

FIG. 3C illustrates the solder transfer system of FIG. 3B with soldertransferred from the intermediate structure to the bump core of the flipchip.

FIG. 3D illustrates the chip bump that results from removing thesubstrate from the portion of the flip chip shown in FIG. 3C.

FIG. 3E is a top view of the chip bump shown in FIG. 3D after a crosssection was taken along a plane that is parallel to the upper surface ofthe flip chip and that includes the line labeled E in FIG. 3D

FIG. 4A is a top view of an example electronic device such as a packagecarrier or a printed circuit board.

FIG. 4B is a cross section of the electronic device shown in FIG. 4Ataken along the line labeled B in FIG. 4A.

FIG. 5A illustrates an attachment system that includes the portion ofthe flip chip of FIG. 3D aligned with the portion of the electronicdevice illustrated in FIG. 4D.

FIG. 5B illustrates the attachment system of FIG. 5A after reflow of thesolder layer.

FIG. 5C is a top view of the electronic device with the flip chipattached to the electronic device.

FIG. 6A is a cross section of the solder transfer system of FIG. 3Busing a multilayer bump core such the multilayer bump core of FIG. 1D.

FIG. 6B is a cross section of a chip bump formed from the soldertransfer system of FIG. 6A.

FIG. 6C is a cross section of an attachment system that includes anelectronic device attached to a flip chip by a chip bump such as thechip bump of FIG. 6B.

DETAILED DESCRIPTION

A flip chip includes one or more chip bumps. Before attachment of theflip to an external device, the chip bumps include a solder layer on abump core. The flip chip can be attached to the external device suchthat the solder layer is bonded with contact pads on both the flip chipand the external device. The attachment provided by the solder layer ismore tolerant of stress than the attachment provided by thethermocompression used in the prior art.

In some instances, the attachment of the flip chip and the externaldevice is performed without substantially changing the shape of the bumpcore but with the bump core spanning the resulting gap between the flipchip and the external device. As a result, the height of the bump coredetermines the distance of separation between the flip chip and theexternal device. The height of the bump cores on the flip chip can beselected so as achieve a particular separation between the flip chip andthe external device. Accordingly, the chip bumps provide a more reliablebond between the flip chip and the external device while also providingcontrol of the resulting separation between the flip chip and theexternal device.

The chip bumps can be formed using a flip chip precursor that includesone or more bump cores in the locations where the chip bumps will beformed. An intermediate structure is also used in the formation of thechip bumps. The intermediate structure includes one or more solderlayers patterned on the flat surface of a substrate. The solder layersare transferred from the substrate onto the bump cores such that thesolder layers serve as the solder layers of the chip bumps. Theintermediate structure allows the solder layers to be formed on a flatsurface rather than directly on the bump cores. The formation of thesolder layers on the flat surface has provided a much more uniformsolder layer thickness than can be achieved when forming the solderlayers directly on the bump cores. The increased thickness uniformityincreases the reliability of the resulting chip bumps. Additionally, thesolder layers can be transferred to the die of a single flip chip. Incontrast, prior method of forming solder bumps generally form the solderbumps on all of the dies included in a wafer. The ability to form thechip bumps on a smaller sample of dies reduces the costs andcomplexities associated with screening different solder materials foruse with a particular combination of flip chip and external device.

FIG. 1A is top view of a flip chip. FIG. 1B is cross section of the flipchip shown in FIG. 1A taken along the line labeled B in FIG. 1A. Thechip includes multiple contact pads 10 on a die 12. Suitable materialsfor the contact pads 10 include, but are not limited to, aluminum.Suitable dies 12 include or consist of one or more materials selectedfrom a group consisting of silicon, gallium nitride, and galliumarsenide. Although not illustrated, the contact pads 10 can be inelectrical communication with one or more electrical circuits on the dieand/or electrical components on the die 12. For instances, examples ofsuitable flip chips include, but are not limited to, integrated circuitchips, microelectromechanical systems (MEMs), photonic integratedcircuits (PIC), and transimpedance amplifiers (TIA).

FIG. 1C illustrates a bump core 14 formed on the contact pad 10 of FIG.1B such that the contact pad 10 is between the bump core 14 and the die12. Although FIG. 1C illustrates the bump core 14 as constructed from asingle layer of material, however, the bump core can be constructed ofmultiple layers of materials stacked as illustrated in FIG. 1D. Multiplelayers of material can be stacked on a contact pad 10 to provide thebump core 14 with the desired height. For instance, the bump core can beformed by stacking gold studs until the bump core 14 has the desiredheight. A suitable height for the bump core 14 includes a height ofgreater than 0.1 mils (thousandths of an inch) or 0.7 mils above thecontact pad 10 and/or less than 10.0 mils or 50 mils above the contactpad 10. The bump core also has a width or diameter labeled D in FIG. 1C.A suitable width or diameter for the bump core 14 includes a width ordiameter greater than 0.1 mils or 0.7 mils, and/or less than 3.0 mils or20 mils.

When a bump core 14 includes or consists of multiple layers of material,the different layers can be the same or different materials. One or morelayers of material in the bump cores 14 can be formed on the contact pad10 using Cu pillars, or Au pillars or with techniques such as wirebondgold ball bumping. In some instances, the bump core 14 includes orconsists of an electrically conducting material such as a metal. Thebump core 14 can have a melting point between the melting point of thedie 12 and the melting point of a solder layer that is discussed in moredetail below. Suitable bump cores 14 can have a melting point greaterthan 375° C. and/or less than 1,250° C. Suitable materials for the bumpcore 14 and/or for layers of material in the bump core 14 include, butare not limited to, metals and/or metal alloys that include or consistof gold, aluminum and copper.

FIG. 2A and FIG. 2B illustrates an intermediate structure 16 for use informing a chip bump 24 on the flip chip. FIG. 2A is a top view of theintermediate structure 16. FIG. 2B is a cross section of theintermediate structure 16 shown in FIG. 2A taken along the line labeledB in FIG. 2A. The intermediate structure 16 includes one or moretransfer pads 18 on a substrate 20. The transfer pads 18 can include orconsist of a solder paste. Solder paste generally includes or consist ofsolder suspended in flux. Suitable solders for the transfer pads 18 aremetal alloys with a melting point less than the melting point of the die12 and/or of the bump core 14. In some instances, the transfer pad 18has a melting point less than 340° C. or 317° C. and/or greater than160° C. or 183° C. Example materials for the solder, include, but arenot limited to, solders that include or consist of tin and lead, soldersthat include or consist of tin and gold, and solders that include orconsist of tin, silver and copper such as SAC solders including SAC 105,SAC387, solders that include or consist of indium and lead. Thesubstrate 20 can include or consist of one or more layers of material.At least the portion of the substrate 20 that contacts the solderincludes or consists of one or more materials selected from the groupconsisting of glass and ceramic.

The position of the transfer pads 18 on the substrate 20 mirrors thepositions of at least a portion of the bump cores 14 on the flip chip.For instance, the transfer pads 18 are arranged such that the flip chipcan be positioned over the intermediate structure 16 with the transferpads 18 aligned with the bump cores 14. As an example, the transfer pads18 can be arranged such that the flip chip can be positioned over theintermediate structure 16 with the center of each bump core over thecenter of one of the transfer pads 18. FIG. 3A illustrates a soldertransfer system that includes the portion of the flip chip of FIG. 1Caligned with the portion of the intermediate structure 16 shown in FIG.2B. The flip chip is inverted over the intermediate structure 16 withthe bump core positioned over the solder contact pad 10. For instance, aline can be drawn that is perpendicular to a surface of the die 12 andthat extends through both the bump core 14 and the aligned transfer pad18. In some instances, the line can extend through both the center ofthe bump core 14 and the center of the aligned transfer pad 18.

A suitable method of forming the transfer pads 18 on the substrate 20includes, but is not limited to, solder printing, and solder dispensing.Solder printing can be an automated, semi-automated, or manual printingprocess. A stencil with the desired pattern is positioned on thesubstrate and the solder paste is positioned on the stencil. A blade iswiped across the stencil so as to fill openings through the stencil withthe solder paste. The stencil is lifted off the substrate leaving thesolder paste on the substrate in the desired pattern.

The one or more transfer pads 18 on the intermediate structure 16 can beplaced in proximity of the one or more bump cores 14 on the flip chip orbrought into contact with the one or more bump cores 14 on the flipchip. For instance, FIG. 3B illustrates the solder transfer system ofFIG. 3A with the intermediate structure 16 contacting the flip chip. Inparticular, the bump core 14 contacts the aligned transfer pad 18.Pressure can optionally be applied in the direction of the arrow labeledP in FIG. 3B.

The one or more transfer pads 18 on the intermediate structure 16 can betransferred from the intermediate structure 16 to the flip chip. Inparticular, the one or more transfer pads 18 on the intermediatestructure 16 can each be transferred from the intermediate structure 16to a bump core 14 on the flip chip such that each transfer pad 18 formsa solder layer 25 on the bump cores 14. For instance, the temperature ofthe transfer pads 18 and/or the intermediate structure 16 in the soldertransfer system of FIG. 3B can be elevated such that the solder reflowsonto the bump core 14 as shown in the solder transfer system of FIG. 3C.The solder layer 25 can be in direct contact with the bump core 14.

The substrate 20 can be removed from contact and/or proximity with theflip chip to provide one or more chip bumps 24 on the flip chip. Forinstance, FIG. 3D illustrates the chip bump 24 that results fromremoving the substrate 20 from the portion of the flip chip shown inFIG. 3C. The resulting chip bump 24 has multiple layers of differentmaterial. For instance, the chip bump 24 includes or consists of thesolder layer 25 on the bump core 14. The solder layer 25 can extend fromthe top of the bump core 14 down to the die 12. Additionally oralternately, the solder layer 25 can surround the bump core 14. Forinstance, FIG. 3E could be a top view of the chip bump 24 shown in FIG.3D after a cross section is taken along a plane that is parallel to theupper surface of the flip chip and that includes the line labeled E inFIG. 3D. The resulting top view shows the solder layer 25 surroundingthe bump core 14. Additionally, the solder layer 25 can be positionedover the bump core 14 such that there are no pores, channels or otherrecesses extending through the solder layer 25. For instance, the solderlayer 25 can be positioned over the bump core 14 such that none of thebump core 14 is exposed to the atmosphere in which the flip chip ispositioned.

A thickness of the solder layer 25 on the solder bump is labeled T inFIG. 3C. A suitable thickness for the solder layer 25 includes, but isnot limited to, a thickness greater than 0.01 mils or 0.5 mils and/orless than 3.0 mils or 10 mils. The method of forming a solder layer 25on the bump core 14 illustrated in FIG. 1A through FIG. 3E is suitablefor forming chip bumps 24 having solder layers 25 with a thickness inthis range. The method illustrated in FIG. 3A through FIG. 3E can besequentially repeated. As a result, a thicker solder layer 25 can beformed on a bump core 14 by sequentially transferring transfer pads 18from multiple intermediate structures 16 to a bump core 14. Additionallyor alternately, transfer pads 18 sequentially transferred to a bump core14 can be different materials. As a result, the solder layer 25 caninclude different layers of different materials. The use of theintermediate structure 16 to form the solder layers 25 on the bump cores14 has proven to provide a surprisingly consistent thickness of solderlayer 25 on the bump core 14.

In some instances, the chip bumps 24 are used as Controlled CollapseChip Connection bumps (C4 bumps). For instance, the chip bumps 24 can beused to connect the flip chip to an electronic device. FIG. 4A is a topview of an example electronic device 26 such as a package carrier, aprinted circuit board, or a lead frame. FIG. 4B is a cross section ofthe electronic device 26 shown in FIG. 4A taken along the line labeled Bin FIG. 4A. The electronic device 26 includes device contact pads 28 ona support 30. The electronic device 26 optionally includes conductors 32on the support 30. In some instances, the conductors 32 can provideelectrical communication between the device contact pads 28 and otherelectrical circuitry (not shown) and/or electrical components on thesupport 30.

The position of at least a portion of the device contact pads 28 on thesupport 30 mirrors the positions of at least a portion of the chip bumps24 on the flip chip. For instance, the device contact pads 28 arearranged such that the flip chip can be inverted and positioned over thedevice with the device contact pads 28 aligned with the chip bumps 24.As an example, the device contact pads 28 can be arranged such that theflip chip can be positioned over the device with the centers of at leasta portion of the chip bumps 24 each being located over a center of oneof the device contact pads 28. As an example, FIG. 5A illustrates anattachment system that includes the portion of the flip chip of FIG. 3Daligned with the portion of the electronic device 26 illustrated in FIG.4D. The flip chip is inverted over the electronic device 26 with thechip bump 24 positioned over a device contact pad 28. For instance, aline can be drawn that is perpendicular to a surface of the electronicdevice 26 and that extends through both the chip bump 24 and the aligneddevice contact pad 28. In some instances, the line can extend throughboth the center of the chip bump 24 and the center of the aligned devicecontact pad 28.

The one or more device contact pads 28 on the electronic device 26 areplaced in contact with the one or more chip bumps 24 on the flip chip.For instance, FIG. 5A illustrates the electronic device 26 in contactwith the flip chip. In particular, the chip bump 24 contacts the aligneddevice contact pad 28. Pressure can optionally be applied to the flipchip and/or electronic device so as to compress together the flip chipand electronic device. For instance, pressure can be applied to the flipchip in the direction of the arrow labeled P in FIG. 5A while theelectronic device is held stationary.

The solder in the one or more chip bumps 24 can be used to attach theflip chip to the electronic device 26. For instance, the temperature ofthe chip bumps 24 and/or the flip chip in the attachment transfer systemof FIG. 5A can be elevated such that the solder layer 25 reflows and isthen cooled such that the solder from the solder layer 25 forms a soldermember 38 that attaches the flip chip and the electronic devices 26 asshown in FIG. 5B and FIG. 5C. FIG. 5B illustrates the attachment systemof FIG. 5A after reflow of the solder layer 25. FIG. 5C is a top view ofthe electronic device 26 with the flip chip 8 attached to the electronicdevice 26. The solder layer 25 can be selected such that the solderlayer 25 has a lower melting point than the bump core 14. As a result,the temperature to which the solder is exposed during reflow canoptionally be between the melting point of the solder layer 25 and themelting point of the bump core 14. This arrangement of material meltingpoints allows full or partial reflow of the solder layer 25 withoutmelting the bump core 14. This reflow does not occur during the priorthermocompression processes.

The chip bump 24 can provide an electrical and/or mechanical connectionbetween the flip chip and the electronic device 26. As is evident fromFIG. 5B, the solder member 38 can contact both the flip chip and theelectronic device 26. Although not shown in FIG. 5A or FIG. 5B, thesolder member 38 can continue to surround the bump core 14 asillustrated in FIG. 3E. The material for the solder can be selected suchthat the solder member 38 is electrically conductive. Additionally oralternately, the bump core 14 can be constructed such that the bump core14 is electrically conducting. As a result, the bump core 14 and/or thesolder member 38 can provide electrical communication between a devicecontact pad 28 and a contact pad 10 on the flip chip.

In FIG. 5A, the solder layer 25 of the chip bump 24 contacts the devicecontact pad 28 and also contacts the contact pad 10 on the flip chip.However, the solder layer 25 is between the bump core 14 and the devicecontact pad 28 such that the bump core 14 does not contact the devicecontact pad 28. In contrast, in FIG. 5B, the bump core 14 contacts thedevice contact pad 28. Compression of the attachment system as discussedabove can cause movement of the flip chip and the electronic device 26toward one another in response to the reflow of the solder layer 25.Alternately, before reflow of the solder layer 25, the compression canbe sufficient for the top of the bump core 14 to penetrate the solderlayer 25 such that the bump core 14 comes into contact with the devicecontact pad 28. Additionally or alternately, the level of compressioncan be sufficient for the bump core 14 to become deformed as a result ofthe compression. The level of compression that deforms the bump core 14can be applied before, during and/or after reflow of the solder layer25. As a result, the deformation of the bump core 14 can be entirely aresult of the compression or can be a combination of the compression andthe elevated temperature. For instance, the temperature used to providereflow of the solder layer 25 can be sufficient to provide full orpartial melting of the bump core 14. Deformation of the bump core 14combined with contact between the device contact pad 28 and the bumpcore 14 allows the bump core 14 to become bonded to both the devicecontact pad 28 and the contact pad 10 of the flip chip. Accordingly, thebump core 14 can also take part in bonding the flip chip and theelectronic device 26.

As is evident in FIG. 5B, in some instances, the bump core 14 contactsthe contact pad 10 and the device contact pad 28 and accordingly spansthe distance between the flip chip and the electronic device 26. As aresult, the height of the bump core 14 can determine the separationbetween the flip chip and the electronic device 26. Accordingly, the oneor more bump cores 14 on a flip chip can be formed with a height that isdesired for the separation between the flip chip and the electronicdevice 26 (labeled S in FIG. 5B). When the bump core 14 becomes deformedduring the attachment of the flip chip and the electronic device 26, theseparation between the flip chip and the electronic device 26 is lessthan the height of the bump core 14 before attachment. Increasing thedegree of deformation of the bump core 14 can decrease the level ofseparation between the flip chip and the electronic device 26. In someinstances where deformation of the bump core 14 occurs, the separationbetween the flip chip and the electronic device 26 is greater than 30%or 50% and/or less than or equal to 100% of the height of the bump core14 before attachment of the flip chip and the electronic device 26. Thechip bumps 24 can be constructed to provide separation between the flipchip and the electronic device 26 that is greater than 0.1 mil, or 1.0mil and/or less than 5.0 mil or 50 mil.

A solid underfill 40 can optionally be located in the space between theflip chip and the electronic device 26. Suitable underfills 40 includeelectrically insulating adhesives. Examples of suitable underfills 40include, but are not limited to, U8410-133 and/or U8439-105 availablefrom Namics Corporation located in Niigata City, Japan.

The electronic device 26 can be a Printed Circuit Board (PCB).Accordingly, the support 30 can be a single layer or multi-layersubstrate of a Printed Circuit Board (PCB). Additionally, the devicecontact pads 28 and the electrical conductors 32 can be the pads andconductive tracks or traces on a Printed Circuit Board (PCB).Alternately, the electronic device 26 can be a package carrier or a chipcarrier. For instance, the electronic device 26 can be a lead framepackage carrier or substrate package carrier. In some instances, theelectronic device 26 is a lead frame. In these instances, the devicecontact pads 28 can be the leads of a lead frame and the support 30 neednot be included in the electronic device 26. Suitable materials for thedevice contact pads 28 include, but are not limited to, plated Au,solder on pad (SOP), and organic solder preserve (OSP).

Although the solder transfer system and the attachment system areillustrated with the bump core having a single layer of material, thesolder transfer system and the attachment system can employ a multilayerbump core. For instance, FIG. 6A illustrates the solder transfer systemof FIG. 3B using the multilayer bump core of FIG. 1D. FIG. 6BIllustrates the chip bump formed from the solder transfer system of FIG.6A. FIG. 6C illustrates an attachment system that includes an electronicdevice attached to a flip chip by a chip bump such as the chip bump ofFIG. 6B.

Although the attachment of the flip chip to the electronic device 26 isgenerally disclosed in the context of a single chip bump 24, multiplechip bumps 24 are often used in attachment of a flip chip and anelectronic device 26. For instance, a chip bump 24 can be formed on eachof the contact pads 10 illustrated in FIG. 1A and each of these chipbumps 24 can be used to bond the flip chip illustrated in FIG. 5C to theelectronic device 26 illustrated in FIG. 5C.

Flip chip dies 12 are generally processed in wafers that often includemore than 10 or even more than 1000 dies 12 on a single chip. The dies12 are then separated from one another through processes such as dicing.The bump cores 14 can be formed on the dies 12 while the dies 12 arestill included in the wafer or can be formed on one or more of the dies12 after the one or more dies 12 has been separated from other dies 12included in the wafer. Additionally or alternately, the solder layers 25can be transferred from the intermediate structure 16 to one or more ofthe dies 12 after the one or more dies 12 has been separated from otherdies 12 included in the wafer. As a result, chip bumps 24 can be formedon different dies 12 with the chip bumps 24 on different dies 12 havingdifferent materials in the solder layers 25. The different flip chipscan then be attached to different electronic devices 26 as disclosedabove. The resulting devices and/or chip bumps can then be tested forfeatures such as bond strength, durability. The resulting devices and/orchip bumps can also be tested for bonding features such as thesolubility of the solder member or solder layer in the bump core and/orfor the solubility of bump core in the solder member or solder layer.Increasing the concentration of the bump core in the solder layer orsolder member can affect the quality of the result. For instance, whengold dissolves in the tin of a solder layer, the resulting solder membercan be undesirably brittle. Prior methods of forming solder bumps on aflip chip generally form the solder bumps on all of the dies 12 includedin a wafer. The ability to form the chip bumps 24 on a smaller sample ofdies 12 reduces the costs and complexities associated with screeningdifferent solder materials for use with a particular combination of flipchip and external device.

Although the above methods and structures are disclosed in the contextof attaching flip chips and external devices, the above methods can beused to attach other types of devices. For instance, one or more chipbumps constructed as disclosed above can provide an electrical and/ormechanical connection between contact pads on two different devicesneither of which is a flip chip. For instance, the one or more chipbumps constructed as disclosed above can provide a mechanical connectionbetween contact pads on two different optical devices.

Other embodiments, combinations and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

1. A flip chip system, comprising: a contact pad on a die; a chip bumpon the contact pad, the chip bump including a solder layer on a bumpcore.
 2. The flip chip system of claim 1, wherein the solder layer has amelting point between a melting point of the die and a melting point ofthe bump core.
 3. The flip chip system of claim 1, wherein the chip bumpis not connected to an external device other than the contact pad. 4.The flip chip system of claim 1, wherein the chip bump is constructedsuch that a plane parallel to a surface of the die and extending throughthe chip bump exposes a cross section where the solder layer surroundsthe bump core.
 5. The flip chip system of claim 1, wherein the chip bumpattaches the flip chip to an electronic device.
 6. The flip chip systemof claim 1, wherein solder layer contacts the contact pad and a secondcontact pad on the electronic device.
 7. The flip chip system of claim6, wherein the solder layer surrounds the bump core.
 8. A method offorming a flip chip system, comprising: obtaining a chip having a bumpcore on a die; obtaining an intermediate structure having a transfer padon a substrate; and transferring the transfer pad from the substrate tothe bump core such that the transfer pad becomes a solder layer on thebump core.
 9. The method of claim 8, wherein transferring the transferpad from the substrate to the bump core includes removing the substratefrom the transfer pad.
 10. The method of claim 8, wherein transferringthe transfer pad from the substrate to the bump core includes reflowingthe transfer pad.
 11. The method of claim 8, wherein the solder layercontacts the bump core after transferring the transfer pad from thesubstrate to the bump core.
 12. The method of claim 8, wherein the bumpcore is positioned on a contact pad on the die.
 13. The method of claim8, wherein the bump core is positioned on a contact pad on the die. 14.The method of claim 8, wherein the bump core has a melting point betweena melting point of the solder layer and the die.
 15. The method of claim8, wherein obtaining the intermediate structure includes solder printingthe transfer pad onto the substrate.
 16. The method of claim 8, furthercomprising: bonding the chip bump to an electronic device aftertransferring the transfer pad from the substrate to the bump core. 17.The method of claim 16, wherein the solder layer contacts a contact padon the on the electronic device.
 18. The method of claim 17, wherein thesolder layer surrounds the bump core.
 19. The method of claim 16,wherein the bump core layer contacts a contact pad on the on theelectronic device.
 20. The method of claim 16, wherein bonding the chipbump to the electronic device includes reflowing the solder layerwithout reflowing the bump core.